Hurley etal
hydrophones



June 28, 1966 T. P. HURLEY ET AL 3,258,739

HYDROPHONES 2 Sheets-Sheet 1 Filed Sept. 10, 1963 FIGI Fl 6. 2 INVENTORS THOMAS P. HURLEY BY NOEL c. SEARS WWW THEIR ATTORNEYS June 28, 1966 T. P. HURLEY ET AL 3,258,739

HYDROPHONE S Filed Sept. 10, 1963 2 Sheets-Sheet 2 INIE'NTOES TJZOMaISPHarZeJ BY Noel C Sears mM/E ATTORNEYS United States Patent 3,258,739 HYDROPHONES Thomas P. Hurley, Bennington, Vt., and Noel C. Sears, Becket, Mass., assignors to Sprague Electric Company, North Adams, Mass., a corporation of Massachusetts Filed Sept. 10, 1963, Ser. No. 307,934 4 Claims. (Cl. 340-) This invention relates to piezoelectric hydrophones and more particularly to such hydrophones employing in a line two or more individual assemblies separated by lengths of cable.

A common cause of failure in a hydrophone is disruption of a cable seal allowing water to enter, resulting in a low resistance path which makes the hydrophone inoperative. This occurs because of (1) vibration during aircraft travel prior to launching, (2) shock associated with impact with the water, and also when the cable is stretched out to its maximum length, (3) constant change in motion of the water, and/ or (4) high hydrostatic pressure at great depths. I

It is therefore an object of the invention to present a compact hydrophone element having securely attached leads.

A further object is to present a piezoelectric hydrophone capable of withstanding vibration, impact and lead tension without breaking the lead-wire connection.

Another object is to provide maximum pull strength, i.e. of the cable itself, against the water seal.

Still another object is to present a very long leakage path for water entering by capillary action along the cable jacket in the event the seal at the cable egress be torn or otherwise disrupted.

Yet another object is to provide a solid monolithic structure around the entire area of the active electrical circuit, eliminating any pockets of differential pressure.

A still further object is to provide a hydrophone wherein hydrostatic pressure will effect a tighter seal at the lead egresses.

Yet a further object is to provide all of the above advantages in a miniature, high sensitivity, high capacitance hydrophone employing a thin-walled, hollow cylindrical piezo-electric element.

Still another object is to provide a multi-element line hydrophone capable of being stacked in a compact stowage, and which when strung out in vertical hang in the water, will all be oriented alike and be in the direction of maximum vertical pull strength.

These and other objects and advantages of the present invention will be made obvious to those skilled in the art by the following description when considered in relation to the accompanying drawing, of which:

FIGURE 1 is a perspective view of the piezoelectric element showing the position of the conacts of the cable to the inner and outer electrodes; and

FIGURE 2 is a perspective view of the encapsulated element.

FIGURE 3 is a perspective view of another embodiment of the present invention.

FIGURE 4 is a perspective view of a plurality of encapsulated units.

The hydrophone component of the present invention comprises a piezoelectric tube having metallic electrodes on its inner and outer surfaces. One lead of a cable is in electrical communication with the inner electrode, and at a point adjacent this connection the other lead is in electrical communication with the outer electrode. The cable circumscribes the periphery of the tube at least once, said cable being tangent to said tube at a point remote from the lead connections. The tube and circumscribing cable, including small lengths of said cable where it passes itself "Ice at the point of tangency, being encapsulated in an elas tomer. Although the cable is shown wrapped around the unit only once, it is to be understood that there may be several turns. The cable can be any of a number of conventional types, e.g. coaxial, unshielded, parallel, twisted, etc. It may consist of two or more conductors.

Referring to the drawing, FIGURE 1 shows a hollow cylindrical piezoelectric element 1 having an inner 2 and outer 3 metallic electrode. The inner electrode has a bridge or passover 4 to the outer surface to facilitate lead connection. A non-electroded area 5 separates the bridge from the outer electrode. One lead of a twin lead cable 6 is shown soldered at 7 to the bridge or passover 4, while the other lead is soldered at 8 to the outer electrode 3.

FIGURE 2 shows the unit of FIGURE 1 encapsulated in an elastomer 10. This encapsulation extends along small lengths of the lead cable as shown at 9.

The piezeolectric material can be any of the prior art materials, preferably barium titanate or the same modified with known additives. The electrode metal can be any of the commonly used materials, e.g. silver, the platinum metals, etc. The leads may be attached to the electrodes by any means which will result in electrical communication, e.g. solder, conductive adhesive, etc. The elastomer includes, natural, reclaimed, vulcanized, synthetic rubber, or polyurethanes of a Shore A durometer reading of 30 to 80.

The elastomer jacket material acts as a waterproof coating and more particularly it provides a pressure-actuated seal about the cable at the points of egress of the cable from the unit. While not essential for successful sealing it has been found that the tapered design, as shown at 9 in FIGURE 2, has greater lead flexibility which permits a smaller diameter stowage stack.

The present invention is not limited to the internal construction shown in FIGURE 1. This is merely a preferred embodiment. The active piezoelectric element can be of any physical shape, e.g. disc, square or rectangular, spherical, hemispherical, triangular, etc. Regardless of the shape of the active element it will be adjacent to a metal or non-metal tube or hollow cylinder. It is to be understood that adjacent to includes surrounded by which is preferred in most cases. The twin lead cable will be electrically communicated to the electrodes and then circumscribed at least once about the adjacent tube or cylinder. The unit will then be encapsulated with the elastomer as previously described. This embodiment is illustrated in FIGURE 3.

FIGURE 3 shows a piezoelectric plate 11 having electrodes 12 and 13 on opposite sides thereof. Surrounding the electroded plate is a hollow ceramic cylinder 14. The electroded plate, which is the active element herein, is supported within the cylinder by means not shown. One lead of a twin lead cable 15 is shown soldered at 16 to electrode lead wire 17. The other lead of twin lead cable 15 is soldered at 18 to electrode lead wire 19. Leads 17 and 19 are soldered to electrodes 12 and 13 respectively. The cable circumscribes the tube and is tangent to the tube at a point about opposite the solder points.

In use a plurality, i.e. two or more, of assemblies is usually employed. They are linked together by means of the cable. This is illustrated by FIGURE 4 which shows string of units 20 linked together by cable 15. The bottom assembly in the spring tends to be misaligned with respect to the other assembly or assemblies if a compensating weight or dummy assembly is not suspended from this bottom assembly. Therefore, it is preferred that the bottom assembly be provided with a trailing end of cable so that the compensating weight can be attached thereto.

Although the external design of the assembly has been shown to have roughly the shape of a cylinder or hockey puck, it is clear that other designs, which would be of greater advantage in the constantly moving sea, are contemplatedt As is evident from the foregoing, the invention is not to be limited to formation of the rather specific illustrative device. Modifications and variations, particularly as to shape, as well as the substitution of equivalents, may be made without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. A device of the type described comprising a piezoelectric tube having metallic electrodes on its inner and outer surfaces, one lead of a cable being in electrical communication with the inner electrode, and at a point adjacent this connection another lead being in electrical communication with the outer electrode; the cable circumscribing the periphery of the tube at least once, said cable being tangent to said tube at a point remote from the lead connections, said tube and circumscribing cable, including small lengths of said cable where it passes itself at the point of tangency, being encapsulated in an elastomer.

2. A device of the type described comprising a hollow cylindrical piezoelectric element having metallic electrodes on its inner and outer surfaces, the inner electrode being bridged over at one point to the outer surface to facilitate lead contact; one lead of a cable being in electrical communication with the inner electrode bridge, and at a point near this contact another lead being in electrical communication with the outer electrode; said cable circumscribing the periphery of the element at least once, said cable being tangent to said element at a point remote from the lead contacts, said element and circumscribing cable, including small lengths of said cable where it passes itself at the point of tangency, being encapsulated in an elastomer.

3. A device of the type described comprising a plurality of hollow cylindrical piezoelectric elements each having an inner and outer metallic electrode, the inner electrode being bridged over at one point to the outer surface to facilitate lead contact, one lead of an interlinking cable being in electrical communication with each of the inner electrode bridges, and at a point near the inner contact another lead being in electrical communication with each of the outer electrodes; said cable circumscribing the periphery of each cylindrical element at least once, said cable being tangent to said elements at a point remote from the lead contacts; said cylindrical elements and circumscribing cable, including small lengths of said cable where it passes itself at the point of tangency, being encapsulated in an elastomer.

4. A device of the type described comprising a plurality of piezoelectric members each having a pair of metallic electrodes, an interlinking cable in electrical communication with said electrodes, a hollow cylindrical member adjacent to each of the piezoelectric members, said cable circumscribing said cylindrical member at least once, said cable being tangent to said cylindrical member at a point remote from the lead connections, said piezoelectric members, cylindrical membcrs and circumscribing cable, including small lengths of said cable where it passes itself at the point of tangency, being encapsulated in an elastomer.

References Cited by the Applicant UNITED STATES PATENTS 1/1956 Miller. 1/1956 Camp. 

4. A DEVICE OF THE TYPE DESCRIBED COMPRISING A PLURALITY OF PIEZOELECTRIC MEMBERS EACH HAVING A PAIR OF METALLIC ELECTRODES, AN INTERLINKING CABLE IN ELECTRICAL COMMUNICATION WITH SAID ELECTRODES, A HOLLOW CYLINDRICAL MEMBER ADJACENT TO EACH OF THE PIEZOELECTRIC MEMBERS, SAID CABLE CIRCUMSCRIBING SAID CYLINDRICAL MEMBER AT LEAST ONCE, SAID CABLE BEING TANGENT TO SAID CYLINDRICAL MEMBER AT A POINT REMOTE FROM THE CONNECTIONS, SAID PIEZOELECTRIC MEMBERS, CYLINDRICAL MEMBER AND CIRCUMSCRIBING CABLE, INCLUDING SMALL LENGTHS OF SAID CABLE WHERE IT PASSES ITSELF AT THE POINT OF TANGENCY, BEING ENCAPSULATED IN AN ELASTOMER. 